The present invention relates to legacy converter filters, and more particularly relates to a legacy converter filter that includes a bandstop filter portion to protect the input circuits of the legacy converter boxes.
Data Over Cable Service Interface Specification (DOCSIS) is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV (CATV) system. It is employed by many cable television operators to provide Internet access over their existing hybrid fiber-coaxial (HFC) infrastructure. In many instances DOCSIS is used to provide video content as well as Internet connectivity and telephone service.
As cable companies migrate from earlier versions of DOCSIS (Data Over Cable Service Interface Specification) to DOCSIS 3 and above, the bandwidth requirement for digital services is ever increasing. This is the case especially in the return band (i.e. upstream band) which in prior versions of DOCSIS such as version 3.0 was limited to the band below 42 MHz. The upstream return band frequency band in DOCSIS 3.0 modems is 5 to 42 MHz. The DOCSIS 3.1 standard moves the upper return band frequency from 42 MHz to 85 MHz in the United States and up to 200 MHz in countries outside the United States.
An issue created when increasing the return path upper frequency is the reuse of the frequency band from 42 to 85 MHz, which is utilized in the United States for channels 2 through 6 on TV set top boxes.
A problem thus arises in that legacy converter boxes that receive channels 2 through 6 are now over driven by the higher signal level produced by the DOCSIS 3.1 equipment return path signals. The higher output DOCSIS 3.1 signals overdrive (i.e. overload) the input tuner of the legacy converter boxes.
Cable companies are also concerned about the insertion loss and return loss in the forward band, 54 MHz to 2 GHz and in some cases 3 GHz. This can affect the quality of service for internet and digital channels. Currently the requirement for having good quality service is from 54 MHz to 1002 MHz and is considered to be normal in the industry. Increasing the upper frequency limit to 2000 MHz allows the cable operators to offer more services on an already cramped system.
There is thus a need for a converter filter that overcomes the problems described supra. In particular, there is a need for a converter filter that includes a bandstop filter portion to protect the input circuits of the legacy converter boxes. The legacy converter filter should also function to pass the forward path (54 MHz to 2 GHz) with minimal loss and reflection.